Hi all, The support in drivers for the V4L2 control API is currently very chaotic. Few if any drivers support the API correctly. Especially the support for the new extended controls is very much hit and miss.
Combine that with the requirements for the upcoming embedded devices that will want to use controls much more actively and you end up with a big mess. I've wanted to fix this for a long time and last week I finally had the time. The new framework works like a charm and massively reduces the complexity in drivers when it comes to control handling. And just as importantly, any driver that uses it is fully compliant to the V4L spec. Something that application writers will appreciate. I have converted the cx2341x.c module and tested it with ivtv since that is by far the most complex example of control handling. The new code is much, much cleaner. The documentation is available here: http://linuxtv.org/hg/~hverkuil/v4l-dvb-fw/raw-file/9b6708e8293c/linux/Documentation/video4linux/v4l2-controls.txt The tree with my code is available here: http://linuxtv.org/hg/~hverkuil/v4l-dvb-fw/ What is very nice is that controls are now exposed in sysfs: $ l /sys/class/video4linux/video0/controls/ audio_crc chroma_gain spatial_chroma_filter_type video_bitrate_mode audio_emphasis contrast spatial_filter video_encoding audio_encoding hue spatial_filter_mode video_gop_closure audio_layer_ii_bitrate insert_navigation_packets spatial_luma_filter_type video_gop_size audio_mute median_chroma_filter_maximum stream_type video_mute audio_sampling_frequency median_chroma_filter_minimum stream_vbi_format video_mute_yuv audio_stereo_mode median_filter_type temporal_filter video_peak_bitrate audio_stereo_mode_extension median_luma_filter_maximum temporal_filter_mode video_temporal_decimation balance median_luma_filter_minimum video_aspect volume brightness mute video_b_frames chroma_agc saturation video_bitrate Writing and reading controls from sysfs is fully transparent and requires no support from the driver. Other highlights: - No need to implement VIDIOC_QUERYCTRL, QUERYMENU, S_CTRL, G_CTRL, S_EXT_CTRLS, G_EXT_CTRLS or TRY_EXT_CTRLS in either bridge drivers or subdevs. New wrapper functions are provided that can just be plugged in. - When subdevices are added their controls can be automatically merged with the bridge driver's controls. - Most drivers just need to implement s_ctrl to set the controls. The framework handles the locking and tries to be as 'atomic' as possible. - Ready for the subdev device nodes: the same mechanism applies to subdevs and their device nodes as well. Sub-device drivers can make controls local, preventing them from being merged with bridge drivers. - Takes care of backwards compatibility handling of VIDIOC_S_CTRL and VIDIOC_G_CTRL. Handling of V4L2_CID_PRIVATE_BASE is fully transparent. There is one thing though that needs to be proven first: can uvc use it as well? The UVC driver is unusual in that it can dynamically add controls. The framework should be able to handle this, but it would be great if Laurent can take a good look at it. BTW, I've also completely overhauled the vivi driver. I've used it to test the control handling, but I took the opportunity to do a big clean up of that driver. The combination of vivi + qv4l2 made testing of the more unusual integer64 and string control types much easier. Regards, Hans -- Hans Verkuil - video4linux developer - sponsored by TANDBERG -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
